The processing of engine and/or vehicle speed signals is fundamental to the operation of today's vehicles. This data is crucial in performing many functions. For example, such information is typically used to control and/or measure various engine operating parameters, such as the engine acceleration, torque, and fuel injection, to name a few.
One example of a specific use of speed data input to a computer for processing is for the servicing and testing of engines. The computer that collects and processes speed signal data, along with other vehicle data, is linked to an SAE (Society of Automotive Engineers) J1587 Bus that operates in accordance with technical specifications set forth in the SAE J1587 standard. The J1587 Bus enables ready access to engine/vehicle data and performance information processed and computed by the computer. This information may then be used to ensure, for example, that the engine meets specifications regarding engine output torque and power requirements.
Various devices have been employed to gather and process speed signals. In U.S. Pat. No. 3,942,365 to Hanson et al., the speed of the engine is measured by a tachometer, which generates an electric pulse for each engine cycle. A computer measures the time periods between pulses to calculate engine speed. In U.S. Pat. No. 4,501,138 to McCandless, a data processor receives the speed signal from an unmounted engine using a frequency to DC voltage converter. The converter is programmed to smooth raw data using the data collected.
It is known in the art that speed signal sensing devices produce noisy speed data, and it is necessary to filter the speed signal data to reduce the noise normally associated with it. One disadvantage associated with filtering engine speed signal data is that such filtering tends to produce filtered data that deviates from the actual engine speed, particularly at the boundaries of the data collection period. This is due to a transient effect associated with the filter, and this effect becomes increasingly pronounced as the data is more heavily filtered. Thus, the filtered data may not be useful over its entire range due to this transient effect, particularly near the data boundaries.
Prior art speed signal processing devices do not adequately address this deficiency with filtered speed signal data. Thus, when testing engine or vehicle speeds, it is necessary to extend data collection periods in order to obtain a sufficient amount of data to measure various performance characteristics that rely on the speed data. This results in longer testing times, which may still yet produce additional corrupted speed data.
What is therefore needed is a technique for gathering filtered engine/vehicle speed signals that addresses the foregoing shortcomings. Such a technique should be reliable, inexpensive to implement, and readily integratable into an existing speed signal processing system.